if the binding type of the NumericTextBox is short or int, the input only allows numeric chars. 

for type decimal for example, input box allows one Letter and the box got red border highlight. user can't enter more letters,  but why is it not behaving the same as type int?

https://demos.telerik.com/blazor-ui/numerictextbox/overview

you can try on the demo link - first 2 input only allows numeric chars.